Universal joint assemblies are well known devices that provide a driving connection between two members adapted to rotate about non-aligned axes of rotation. Universal joint assemblies are widely used between rotatable drive shaft sections in vehicle drive train systems. A typical universal joint assembly includes a cross having a central body portion with four cylindrical trunnions extending outwardly from the cross. The trunnions are oriented in a single plane and extend at right angles relative to one another, and the trunnions have a common intersection at the center of the central body portion. A hollow cylindrical bearing cup is mounted on the end of each of the trunnions. Needle bearings or similar means are provided between the outer cylindrical surfaces of the trunnions and the inner cylindrical surfaces of the bearings to permit relative rotational movement between the trunnions and the bearings. The bearings that are mounted on an opposed pair of the trunnions can be connected to a first end yoke secured to an end of a first drive shaft section, while the bearings that are mounted on a second opposed pair of the trunnions can be connected to a second end yoke secured to an end of a second drive shaft section. A Cardan universal joint is classified as a non-constant velocity type of universal joint because the instantaneous angular velocities of the driving shaft and the driven shaft will vary with the angle of rotation (although the average angular velocities for a complete revolution are equal).
A double Cardan universal joint is a near-constant velocity universal joint that is used to correct some of the deficiencies in a single Cardan universal joint. A typical double Cardan universal joint is essentially formed by two single Cardan universal joints that are connected by a unitary coupling yoke having a supporting and centering mechanism. Thus, a typical double Cardan universal joint includes a first yoke that is connected to a first journal cross, a coupling yoke having a first end that is connected to the first journal cross and a second end that is connected to a second journal cross, and a second yoke that is connected to the second journal cross. The supporting and centering mechanism is usually provided by mating ball and socket portions provided on the first and second yokes. The coupling yoke cooperates with the supporting and centering mechanism so as to generally bisect the angle between the first and second yokes. As a result, near constant velocity operating characteristics are attained during operation.
An alternative known structure for a double Cardan universal joint is known as a twin ball and centering plate type. In such a joint, the first and second journal crosses are connected together by a two-piece flanged coupling yoke. The first piece of the coupling yoke includes a yoke portion that is connected to the first journal cross and a flange portion. Similarly, the second piece of the coupling yoke includes a yoke portion that is connected to the second journal cross and a flange portion. The two flange portions are connected together so as to define an internal cavity, in which a centering plate is slidably disposed. The centering plate includes an inner socket portion that receives the ball portions of the first and second yokes therein and an outer plate portion that is slidably disposed within the cavity defined by the mating flange portions. Although the twin ball and centering plate double Cardan universal joint provides near-constant velocity rotation, it is limited to relatively low rotational speeds due to friction created by the centering plate when operating at an angle. The sliding mechanism in this type of design also tends to lock up when placed under load. This occurs because existing designs have a flat surface of the sliding mechanism in contact with the housing. This flat surface often becomes cocked when load is applied to the centering mechanism due to the inherent looseness between these two pieces, causing the outer edge to dig into the housing. It would be desirable to create a double Cardan universal joint with a centering plate with minimal rotational friction and that resists locking under load.